This invention relates to formation of ethers and more particularly relates to formation of alkyl ethers from alcohols and alkenes using an AMS-1B crystalline borosilicate-based catalyst.
Alkyl ethers are compounds with a general formula R--O--R' where R and R' are alkyl groups. Typically, ethers are neutral, comparatively unreactive compounds having low solubility in water but easily soluble in organic liquids and frequently used as solvents in organic synthesis, plasticizers, anesthetics and fumigants. Methyl t-butyl ether particularly is useful as an octane booster in gasoline.
Conventionally, ethers can be prepared by reaction of an alkyl halide and sodium alcoholate (Williamson synthesis), by dehydration of alcohols with strong acids and by addition of an alcohol to an olefin under acid catalysis such as by sulfuric acid, phosphoric acid, hydrochloric acid and boron trifloride. Methyl t-butyl ether can be made from isobutylene and methanol in the presence of an acidic ion-exchange resin catalyst. Ethers, their preparation, properties and uses are described in Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Vol. 9, pp. 381-393, incorporated by reference herein.
Zeolitic materials, both natural and synthetic, are known to have catalytic capabilities for many hydrocarbon processes. Zeolitic materials typically are ordered porous crystalline aluminosilicates having a definite structure with cavities interconnected by channels. The cavities and channels throughout the crystalline material generally are uniform in size allowing selective separation of hydrocarbons. Consequently, these materials in many instances are known in the art as "molecular sieves" and are used, in addition to selective adsorptive processes, for certain catalytic properties. The catalytic properties of these materials are affected to some extent by the size of the molecules which selectively penetrate the crystal structure, presumably to contact active catalytic sites within the ordered structure of these materials.
Generally, the term "molecular sieve" includes a wide variety of both natural and synthetic positive- ion-containing crystalline zeolite materials. They generally are characterized as crystalline aluminosilicates which comprise networks of SiO.sub.4 and AlO.sub.4 tetrahedra in which silicon and aluminum atoms are cross-linked by sharing of oxygen atoms. The negative framework charge resulting from substitution of an aluminum atom for a silicon atom is balanced by positive ions, for example, alkali-metal or alka- line-earth-metal cations, ammonium ions, or hydrogen ions.
Prior art developments have resulted in formation of many synthetic zeolitic crystalline materials. Crystalline aluminosilicates are the most prevalent and, as described in the patent literature and in the published journals, are designated by letters or other convenient symbols. Examples of these materials are Zeolite A (U.S. Pat. No. 2,882,243), Zeolite X (U.S. Pat. No. 2,882,244), Zeolite Y (U.S. Pat. No. 3,130,007), Zeolite ZSM-4 (U.S. Pat. No. 3,578,723), Zeolite ZSM-5 (U.S. Pat. No. 3,702,886), Zeolite ZSM-11 (U.S. Pat. No. 3,709,979), Zeolite ZSM-12 (U.S. Pat. 3,832,449), Zeolite NU-1 (U.S. Pat. No. 4,060,590) and others.
Boron is not considered a replacement for aluminum or silicon in a zeolitic composition. However, recently a new crystalline borosilicate molecular sieve AMS-1B with distinctive properties was disclosed in U.S. Pat. Nos. 4,268,420 and 4,269,813 incorporated by reference herein. According to these patents AMS-lB can be synthesized by crystallizing a source of an oxide of silicon, an oxide of boron, an oxide of sodium and an organic template compound such as a tetra-n-propylammonium salt. The process of this invention uses AMS-1B crystalline borosilicate molecular sieve.
Hydrocarbon conversion processes are known using other zeolitic materials. Examples of such processes are dewaxing of oil stock (U.S. Pat. Nos. 3,852,189, 4,221,635 and Re. 28,398); conversion of lower olefins (U.S. Pat. Nos. 3,965,205 and 3,960,978 and European patent application Ser. No. 31,675); aromatization of olefins and aliphatics (U.S. Pat. Nos. 3,761,389, 3,813,330, 3,827,867, 3,827,868, 3,843,740, 3,843,741 and 3,914,171); hydrocracking and oligomerization of hydrocarbons (U.S. Pat. Nos. 3,753,891, 3,767,568, 3,770,614 and 4,032,432); conversion of ethane to aromatics and C.sub.3+ hydrocarbons (U.S. Pat. No. 4,100,218); conversion of straight-chain and slightly branched-chain hydrocarbons to olefins (U.S. Pat. No. 4,309,275 and 4,309,276); and conversion of C.sub.4 paraffins to aromatics (U.S. Pat. No. 4,291,182).
A method to manufacture ethers directly from an alkene and an alcohol would be desirable and a method that would form ethers from readily available feedstocks in one step without excessive losses to undesirable by-products would be especially desirable. A process that forms methyl t-butyl ether from methanol and isobutylene would be advantageous.